1. Field of the Invention
The present invention generally relates to the field of nanostructure positioning and orientation on substrates, and more particularly to the field of molecular sized nanoelectromechanical systems (NEMS).
2. Related Art
US PG PUB 20030190278 “Controlled deposition of nanotubes” discloses methods for depositing nanotubes.
Diehl et al. “Self-assembled, deterministic carbon nanotube wiring networks,” Angew. Chem. Int. Ed. 41:353 (2002) disclose a “minimal lithography” technique for chemically assembling small deterministic crossbars of SWNT ropes. Spatial positioning of the SWNTs is induced by an alternating current field.
Yamamoto et al. “Orientation and purification of carbon nanotubes using AC electrophoresis,” J. Phys. D. Appl. Phys. 31: L34-L36 (1998) discloses orientation of nanotubes in isopropyl alcohol. The authors report that other methods for orienting nanotubes exist, such as slicing of a polymer resin matrix containing nanotubes and transferring nanotubes trapped in the pores of a ceramic filter onto a polymer surface.
Rao et al. “Larger-scale assembly of carbon nanotubes,” Nature 425:36 (2003) discloses the assembly of single walled nanotubes (SWNTs) on organic molecular marks applied to a substrate by stamping or lithography. The authors created two distinct surface regions coated either with polar chemical groups or non-polar groups. The SWNTs adhered to the nonolar regions.
Lay et al. “Simple Route to Large-Scale Ordered Arrays of Liquid-Deposited Carbon Nanotubes” Nano Letters 4(4):603-606 (2004) discloses ordered arrays of carbon nanotubes deposited at room temperature from aqueous suspensions onto silanized SiO2 surfaces.
Cumings et al. US 2002/0070426 A1 disclose a method for forming a telescoped multiwall carbon nanotube (“MWCNT”). Such a telescoped multiwall nanotube is shown in this publication to act as a linear bearing in an electromechanical system. That is, the walls of a multiwalled carbon nanotube are concentrically separated and are shown to telescope axially inwardly and outwardly. In Science 289:602-604 (28 Jul. 2000), a scientific publication related to the 2002/0070426 A1 patent publication, Cumings and Zettl describe a low friction nanoscale linear bearing, which operates in a reciprocal (i.e. telescoping) manner.
Den et al. U.S. Pat. No. 6,628,053 discloses a carbon nanotube device comprising a support having a conductive surface and a carbon nanotube, wherein one terminus of the nanotube binds to the conductive surface so that conduction between the surface and the carbon nanotube is maintained. The device is used as an electron generator.
Falvo et al. Nature 397:236-238 (Jan. 21, 1997) disclose studies involving the rolling of carbon nanotubes using atomic force microscope (AFM) manipulation of multiwall carbon nanotubes (MWCNT, termed in the paper “CNT”). No bearing properties are disclosed.
Minett et al. Current Applied Physics 2:61-64 (2002) disclose the use of carbon nanotubes as actuators in which the driving force is obtained from a deformation of the nanotube when a charge is applied. The authors, in their review, also disclose the preparation of a suspended carbon nanotube across two metallic contacts growth of nanotubes across two metal contacts in a process that involved E-beam lithography and selective patterning.
Cumings et al. Nature 406:586 (Aug. 10, 2000) disclose techniques for peeling and sharpening multiwall nanotubes. These sharpened tubes are disclosed as having utility as biological electrodes, microscopic tips, etc.
Fraysse at al. Carbon 40:1735-1739 (2002) discloses carbon nanotubes that act like actuators. In concept, a SWNT may be disposed above a substrate and between a pair of metal-on-oxide layers. The nanotubes act as actuators though a cantilever effect achieved through longitudinal deformation of the nanotube.
Zhao et al. “Nanowire Made of a Long Linear Carbon Chain Inserted Inside a Multiwalled Carbon Nanotube,” Rev. Lett. 90, 187401 (2003), discloses a one-dimensional (1D) carbon structure, carbon nanowires (CNWs), discovered in the cathode deposits prepared by hydrogen arc discharge evaporation of carbon rods.
Fennimore et al. “Rotational actuators based on carbon nanotubes,” Nature 424, 408-410 (2003), discloses rotational actuators based on carbon nanotubes deposited on a substrate.
Recent advances in nanoscale synthesis and fabrication techniques have opened the door to the manufacture of true nanoelectromechanical systems (NEMS). For example, multiwall carbon nanotubes (MWCNTs) have been utilized as key enabling elements for nanoscale electrostatically-driven torsional1 and rotational2 actuators, orders of magnitude smaller than their microelectromechanical (MEMS) counterparts. Due to their small size, robust design and near-perfect atomic structure, such constructs hold great promise as building blocks for complex nanoelectromechanical systems. The utility of individual actuators can be significantly increased by their incorporation into arrays of devices. Such arrays could serve in a variety of applications, including adaptive optics, high frequency mechanical filters, mass sensors, and microfluidic gates and pumps.
A fundamental challenge in the development of NEMS arrays (and of nanotube- and nanowire-based devices in general) is the large-scale controlled placement of molecular sized building blocks on a substrate. Methods based on chemical vapor deposition (CVD) avoid this problem by, for example, growing nanotubes directly on the substrate where they ultimately will be located3. Unfortunately, such methods are unable to produce very high quality multi-walled carbon nanotubes as are often required for NEMS applications2,4. Furthermore, CVD is commonly a high temperature process, which severely limits compatibility with substrate materials or other system components. Hence, there is much interest in low temperature techniques to aid in the selective placement and alignment of prefabricated nanostructures. There has been some progress in developing fluidic techniques for aligning nanowires5 and nanotubes6,7, and various functionalization schemes have been explored for placing nanotubes on particular areas of a substrate8-10. Unfortunately nearly all of these methods necessitate rather complex substrate topology or involved and limiting chemistry.